Curved metal plates and method and apparatus for making same



Jan. 10, 1967 M. s. MUNFORD CURVED METAL PLATES AND METHOD AND APPARATUS FOR MAKING SAME Filed Oct.

3 Sheets-Sheet 1 fol INVENTOR MARVIN S. MUNFORD DJ/LQMA/ C. ML

ATTORNEY Jan. 10, 1967 M. s. MUNFORD 3,297,498

. CURVED METAL PLATES AND METHOD AND APPARATUS FOR MAKING SAME Filed Oct. 1, 1962 3 Sheets-Sheet 2 INVENTQR MARV/N 5. MUN/ ORD ATTORNEY 2\ I 1 A vv r 7. Fl mum .9 5 Lima 0 0 0 0 O O 0 nm O O O a O O O O O O O O O 0 mm mm mm m Y Jan. 10, 1967 M. s. MUNFORD CURVED METAL PLATES AND METHOD AND APPARATUS FOR MAKING SAME 5 Sheets-Sheet 5 Filed 001:. l, 1962 INVENTOR MARVIN 5: MU/VFORD BY {KM C. /j .,--4,,,

ATTORNEY iilfilfid Patented Jan. 16, 1967 3 297,498 CURVED METAL PLATES AND MEG-THEE AND APPARATU FQR MAKENG SAME Marvin S. Mumford, Boulder, (1050., assignor to Bail Brothers Company incorporated, Muncie, Ind, a corporation of Indiana Filed Get. 1, 1962, Ser. No. 227,433 8 Qlairns. (Ql. 148-115) This invention relates generally to metal forming and more particularly to curved metal plates for printing, engraving and photoengraving applications having improved grain properties and dimensionally stabilized properties and to a method and apparatus for forming same.

Ideally, photoengravers would like to be able to obtain blank, preformed metal plates upon which an impression could be transferred, then etched and sold to printers. Unfortunately, blank, curved plates heretofore commercially available have not been entirely satisfactory, principally because the grain size aggregate thereof had been adversely affected and/ or the configuration or shape changed during the burning-in and etching process. Generally, the greatest change occurred during the burning-in process, i.e., the heating of the plate to a temperature of approximately 400 F. The most common type of configuration change was a springing back of the plate, i.e., an increase in the radius of curvature of the plate. Such change in shape detracted from the desirability of using such plates, particularly in connection with high speed rotary printing presses, since they could not be easily or conveniently mounted to exert a substantially even printing pressure across the entire surface thereof. Generally, no matter how much care was observed in mounting these plates on the printing drum almost invariably a portion of the plate was not in contact with the drum. This condition resulted in a pumping or flexing action between the plate and drum with each printing cycle, which greatly decreased the useful life of the plate. Additionally, the use of such a plate adversely affected both the operating efiiciency of the printing press and the quality of the image obtained therefrom. Consequently, most photoengravers have continued to make curved photoengraving plates in the usual manner, i.e., first etching fiat plates and then forming same into the desired configuration. The significance of this is not fully appreciated until it is realized that photoengravers, by adhering to the usual practice, are not only faced with the necessity of maintaining expensive metal forming equipment, but also must tolerate photoengraving plates having images which became distorted and damaged during the forming operation. A method has been discovered, however, and an apparatus devised which, for the first time, permits the formation of blank, preformed metal plates that will not, when etched, undergo any appreciable dimensional change or change in shape and will not appreciably change in grain size, and will have a long printing life.

Accordingly, the primary object of this invention is to provide curved metal plates having improved grain size and dimensionally stabilized properties and a method and apparatus for forming same.

Another object of this invention is to provide a dimensionally stabilized curved metal plate.

Another object of this invention is to provide curved plates for photoengraving application, the shape of which, when etched, remains appreciably unchanged as compared to its pro-etched shape.

Another object of this invention is to provide a method and apparatus for forming for printing, engraving and photoengraving applications, curved metal plates which will not undergo any appreciable dimensional change as a result of being etched.

Another object of the invention is to provide a method and apparatus forforming for photoengraving applications a dimensionally stabilized, curved plate which has at least one surface thereof free from check marks and objectionable grain enlargement.

Another object ofrthis invention is to provide an inexpensive apparatus for producing blank preformed metal plates for photoengraving applications.

Another object of the invention is to provide an apparatus for forming curvedmetal' plates, said apparatus having a forming capability which is substantially unaffected by roller misalignment resulting from wearing of the bearings and the like.

The foregoing and other objects and advantages will become apparent from the specifications and drawings in which: 7

FIGURE 1 is side elevation of an apparatus for forming curved plates for printing applications;

FIGURE 2 is front elevation of the apparatus shown in FIGURE 1;

FIGURE 3 is sectional view taken along line 3-3 of FIGURE 2;

FIGURE 4 is an enlarged sectional elevation of the layer, metal plate, and non-marring, heat resistant layer of material shown in the assembled condition prior to the forming operation; and

FIGURE 5 is a perspective view of a curved plate made in the apparatus illustrated in FIGURES 1-3.

The method and apparatus of the present invention is particularly well suited for curving the very special zinc and magnesium alloys used as photoengraving metals. Plates of these special alloys are formed by closely controlled processes so as to maintain the grain size within certain limits and also to insure that the surface of the plate to be etched is very smooth and free from defects.

It will be readily visualized by those familiar with the art that when a metal plate is curved or bent, certain changes, such as changes in grain size, for example, occur in the metal. Thus, the carefully controlled effect attained during the manufacture of fine photoengraving alloys can be materially altered due to subsequent forming. In accordance with the present invention, it has been determined that the original qualities of the metal can be maintained even through the metal is formed, provided that a careful control of the forming process is maintained so that undue stresses and changes in grain size resulting from the forming, as well as the burning-in process used prior to etching will not deleteriously affect the etching qualities of the alloyed plate. This is accomplished by a careful control of a time-temperature pressure-strain rate relationship in an apparatus suitable for carrying out the method of the invention and producing a product of the invention.

It has been discovered that a plate suitable for photoengraving application can, without adversely affecting the original etching qualities of the plate, be curved into a configuration or shape which will not appreciably change even though the curved plate is subsequently heated to temperatures as high as 400 F. during the burning-in process. This result is achieved by applying pressure to a plate heated to a temperature to permit formation thereof with the surface to be etched being free from check marks and, during the completion of forming of the plate, exerting forming pressure on the plate which has been heated to a temperature within the hot working temperature range for the composition of the plate for a time period such that there is no appreciable change in grain size and no appreciable dimensional change when the plate is subsequently burned-in and etched. An apparatus suitable for achieving this result is illustrated in the drawings in FIGURES 1-3 wherein the apparatus is shown comprising a pair of vertically spaced apart rollers 10 and 11,

a horizontally disposed platen 12, a rotatable cam 13, a roller 14 for supporting the material to be formed, a layer 15 of high tensile strength material, such as stainless steel, upon which is disposed a layer of relatively soft, non-marring, heat resistant material 16, such as sheet asbestos, and an electric motor 17 connected to a source of power (not shown) and in operable driving relationship with roller 10 through a gear box 18, clutch assembly 19, a worm 20, a worm gear 21, and two spur gears 22 and 23, the later of which is mounted on and keyed to the shaft 24 of roller 10.

The platen 12 has mounted on the under surface 12a thereof a plurality of heat means 25 such as strip heaters, which are connected in parallel to a source of electric power (not shown) through a variable transformer 26. For increased flexibility in operation, the strip heaters 25 are preferably temperature adjustable. A thermostat may be substituted for the variable transformer 26, if desired. The rotatable cam 13 which is operated through handle 27 that is connected to one end thereof is disposed above platen 12 and transverse of the longitudinal axis thereof. The rotatable cam 13 has a fiat surface portion 28. In the cams normal position the fiat surface portion 28 is disposed parallel to and spaced apart from the upper surface of platen 12 (FIGURE 3). When cam 13 is in this position the assembled layer 15 of flexible material, metal plate 29 to be formed, and layer of non-marring, heat resistant material 16 (see also FIGURE 4) can easily pass between the cam 13 and platen 12. In the cams actuated or locked condition, preferably being accomplished by rotating handle 27 in a counterclockwise direction (as determined from FIGURE 1), the arcuate surface of the cam 13 is in firm engagement with the upper surface of the layer 15 thereby securely wedging and holding said layer 15 against the upper surface of the platen 12.

The supporting roller 14 is disposed between one end of the platen 12 and the vertically spaced apart rollers 10 and 11. The uppermost surface of said supporting roller 14 is preferably tangent to a line connecting the upper surface of platen 12 and the uppermost surface portion of roller 11.

Roller 10 is used as the forming roller and may be formed from a pipe, preferably of the seamless variety. The outside diameter of roller 10 is equal to the outside diameter of the rotary press printing drum upon which the photoengraved plate is to be used, plus or minus 0.005 inch. The outer surface of roller 16 is uniform to the extent that surface variations thereof do not exceed 0.601 inch per inch. Since undersized curved plates are easier to install on the printing drum of the rotary press than oversized plates, it is preferable that the outside diameter of the forming roller 10 be slightly less than the outside diameter of the rotary press printing drum. Magnesium and zinc alloy plates, formed in accordance with this invention, seldom increase in diameter following burningin and etching and normally are the same size or slightly undersized as compared to their pre-burned-in and etched condition; however, any change in size is well within the tolerance limits of plus or minus 0.005 inch. In actual practice, the outside diameter of roller 10 is formed slightly undersized in order to accommodate the smallest outside diameter of printing roller within a certain size range since with the use of a layer of material of uniform thickness interposed between the outer surface of roller 10 and the inner surface of the plate 29; as a result the inside diameter of the plate can be made larger than the outside diameter of the roller 10, the exact inside diameter of the plate depending on the thickness of the layer of material of uniform thickness used.

Forming roller 10 is preferably hollow and has mounted equally spaced around on the inner surface thereof a plurality of suitable heating means 30, which are preferably temperature adjustable, such as strip heaters. The heating means 30 are connected in parallel to a source of electric power (not shown) through a variable transformer 31.

A thermostat may be substituted in place of the variable transformer 31, if desired. Forming roller 19 has mounted on the outer surface thereof clamping means 32 for securely holding one end or side of the layer 15 against the outer surface thereof. Clamping means 32 comprises a plurality of brackets 33 mounted in pairs, each pair of which is mounted in line with the other pairs and each pair of which is securely attached to the outer surface of the forming roller 10 by suitable means such as screws 34. Each pair of brackets has a rotatable cam 35, referably circular in cross section, eccentrically mounted therebetween on an axle 36. Each cam 35 has a plurality of cylindrically shaped recesses 37 formed in the outer periphery and extending radially inward toward the center of said cam. Operation of each cam 35 is effected by inserting a cylindrical shaft or rod (not shown) into one of the recesses 37 and rotating said rod in the desired direction.

Rollers 10 and 11, supporting roller 14 and rotatable cam 13 are mounted between two side plates 38 and 39 which extend vertically upward from the upper surface 49 of the base 41. A tie bar 42 which is positioned in abutting relation with a portion of the undersurface 12a of platen 12 and also preferably disposed vertically below rotatable cam 13 is fastened to both of the side plates by screws 43 and holds the side plates in fixed spaced apart relation. The reduced diameter portion of each end of forming roller shaft 24 is supported in pillow blocks 44. Each pillow block 44 is disposed between two vertically extending portions 45 and 46 of the side plates 38 and 39 and rests upon a spacer block 47. Each pillow block-spacer unit is removably mounted on its respective side plate by any suitable means such as screws 48. By using spacer blocks of varying heights, flexibility in operation is obtained since forming rollers of varying diameters can be easily installed in the apparatus shown. If desired, the spacer blocks 47 can be dispensed with entirely without affecting the efficiency of the apparatus.

Roller 11 or the satellite roller is mounted in a pair of blocks 49, one of each which is mounted on the inner surface of a respective one of the side plates 38 and 39 by screws 50. A pair of adjusting screws 51, each of which is mounted in a block 52 (FIGURE 3) are mounted at right angles to each other and adjacent to each of the blocks 49. Said adjusting screws 51 are used to ajust the position of the longitudinal axis of the satellite roller 11 to insure that the opposed surfaces of the satellite roller 11 and forming roller 16 are substantially parallel to each other A generally horizontally disposed layer of sheet metal 53 upon which is positioned a layer of suitable insulating material 54 such as asbestos is located beneath roller 11 (FIGURE 3) for the purpose of preventing drafts and minimizing loss of heat from the apparatus.

As shown in FIGURE 4, the front end of layer 15 is sandwiched between two rectangular metal strips 55 and 56 which are securely held together by screws 57. One metal strip 56 is wider than the other strip 55 and is preferably positioned on the under surface of layer 15. In order better to insure against the possibility that the upper surface of layer 15 will not mar or scratch the adjacent surface of metal plate 29, a non-marring, heat resistant layer of material 16 is disposed between the upper surface of layer 15 and metal plate 29. Notches 29a (shown only in FIGURE 5) may ultimately be required to be formed in both sides of metal plate 29 and this is preferably done before the forming operation. In the form normally received by the photoengravers, metal plate 29 may be formed without any previous surface treatments; however, metal plate 29 is normally received with one surface thereof being coated with a protective material 53 such as a thermo-setting phenolic resin (shown in exaggerated thickness in FIGURE 5 only) to insure that said surface is not subjected to the 3 chemical action of the etching solution during the etching process.

Special consideration is given to the design of the top portion of each side plate 38 and 39 to insure that formed plates extending more than 180 around the periphery of the forming roller can be taken off the roller without removing roller 10 from the apparatus. Accordingly, on at least one of the side plates the width of the vertically extending portions 45 and are held to a minimum and the heights to a maximum. A formed plate extending about 230 around the periphery of roller 10 (represented by p in FIGURE 1) can be removed by sliding the plate 29 ofi roller 10 and across idler spur gear 22 and the top of side plate 33 While a formed plate extending about 260 around the periphery of roller it) (represented by p in FIGURE 3) can be taken off the opposite end of roller 10 across side plate 39. Except for the existence of idler spur gear 22 on side plate 33, the same size of formed plate could be taken olf roller 10 across either side plate.

OPERATION Generally, the method of forming curved metal plates according to the invention using the above described apparatus is accomplished by turning on heaters 25 and 3t and warming up the apparatus, preheating metal plate 29 on platen 12, then inserting the assembled layer and layer of heat resistant material 16 tail end first be tween rollers 10 and 11 from the side opposite that on which the platen 12 is located and sliding same underneath plate 29, clamping the front end of layer 15 to the outer surface of forming roller 10 with clamping means 32, rotating forming roller 14 to 'draw the metal plate 29 completely between the rollers 10 and 11, actua ing cam 13 to wedge the trailing end of layer 15 against the upper surface of platen 12 and letting roller 10 continue to turn until the clutch assembly 19 begins to slip at a predetermined torque level, and then maintaining the plate 29 at this forming pressure and the temperature level of the heaters 30 until the plate 2? is dimensionally stabilized such that it will not appreciably change shape even though subsequently heat cycled during the burning-in process.

As previously mentioned, metal plate 29 is preferably preheated by being placed on the heated platen 12. It will be understood, however, that under certain conditions, the use of strip heaters 25 can be dispensed with since the plate 29 can be preheated from the :heat radiating outwardly from the strip heaters 30 positioned within roller 10 as the plate comes into close proximity with roller 10 and also through conduction when the plate passes between rollers 10 and 11. The purpose for preheating the plate is to permit subsequent forming thereof Without incurring any check marks such as stress curving marks in the surface that is to be etched. The existence of any check marks or surface blemishes which are detectable with or without the aid of a 10X handglass or which are detectable only after the etched surface has been chrome plated, as is usually the case with magnesium alloy plates, results in the plate being rejected. A plate which does not have in one of its surfaces any check marks detectable as specified above is considered appreciably free of check marks. It is, of course, unfortunate that some of these check marks are so small that they cannot be detected until after the chrome has been deposited, their existence being ascertained only because the chrome forms an uneven deposit around said defects, since all the work required to produce a photoengraving has been invested in the plate. However, it has been found that such check marks, including those which cannot be detected until after the completion of the chrome plating, can be prevented by properly preheating the plate prior to the forming thereof, thereby increasing the ductility such that the plate can deform plastically without fracturing. The minimum degree of grain refinement thereof.

preheat required thus depends upon the ductility of the plate material and the rate at which the plate is to be deformed. Good forming results have been obtained with a metal plate approximately 0.18 inch thick and containing a minimum of 99 percent by weight of zinc which was preheated to a minimum temperature of about F. and fed between rollers 10 and 11 at a rate of up to approximately twelve inches per minute, forming roller 10 having a seven inch outside diameter. Good results have also been obtained with a metal plate approximately 0.l8 inch thick and containing a minimum of 93.5 percent by weight of magnesium which was preheated to a minimum temperature of about 250 F. and fed between rollers 10 and 11 at a rate up to approximately twelve inches per minute, forming roller 10 having a ten inch outside diameter.

The maximum degree of preheat depends to a great extent upon time the plate is held at such temperature and the rate at which a change in grain size takes place. The working or forming of metal below the recrystallization temperature or the lower limit of the hot working temperature range of the plate material, the hot working temperature range being the temperature range Within which the metal may be deformed without becoming strain hardened, strain hardens the metal and results in However, grain refinement produced in this manner is undesirable since the grains so refined etch at a different rate than the remaining unaffected grains, thereby adversely affecting the quality of the final etched impression. Additionally, plates having substantially nothing but strain hardened grains have been found to be generally unsuitable for high quality photoengraving applications. Heating the plate to a temperature within the hot working temperature range of the plate material can result in grain enlargement, the amount of enlargement being dependent upon the temperature within said temperature range that the metal is maintained and the time said temperature is main- .tained. Since a large grain aggregate etches at a different rate than a small grain aggregate, the quality of the image being thereby atfected, grain growth should be held to a minimum. As a matter of fact, grain size is such an important factor in the production of photoengraving plates that a very high degree of control is exercised to produce plates having the smallest possible grain size such that the grain size resulting from the subsequent forming and burning-in of said plates will be as small as possible so as not to aflfect adversely the etching qualities of the plate. Even so, conventional p-hotoengraving techniques do increase the grainsize sufficiently so as to affect adversely the'quality of the final etching.

.Currently, the average grain diameter and the maximum grain diameter of metal plates as received by photoengravers is approximately 0.001 inch and 0.003 inch, respectively, as determined by the Haynes intercept method. Although the surface of a a plate having a larger average grain diameter than 0.001 inch may be used without adversely affecting the quality of the final etching so long as the maximum diameter does not exceed approximately 0.003 inch, the grain size of commercially available photoengraving plates exceedsthese limits. However, it has been found that a maximum grain diameter of approximately 0.003 inch is not exceeded where a plate which has been preheated prior to forming and then subsequently heated to a temperature within the hot working temperature range of the metal for a period of time sufficient to become dimensionally stabilized such that its shape will not appreciably change during the "burningin process. As a matter of fact, good forming results have been obtained with a metal plate containing a minimum of 99 percent by weight of zinc which was formed at a temperature above 135 F. and then subsequently subjected to the forming pressure and a temperature between approximately 330 F. to 430 F. for a time interval from approximately thirty seconds to about twenty minutes. Beneficial results have also been obtained with a metal plate containing a minimum of 93.5 percent by weight of magnesium which was formed at a temperature above 250 F. and then subsequently subjected to the forming pressure and a temperature between approximately 450 F. to 800 F. for a time interval from approximately thirty seconds to about thirty minutes. During these forming operations, it was observed that the grain size of magnesium was not as sensitive to temperature changes as 'zinc nor did it increase rapidly as zinc.

Concerning in greater detail the operation of the illustrated apparatus, after metal plate 29 has reached its preheat temperature, the time required for a plate about 0.18 inch thick to reach its preheat temperature seldom taking more than about thirty seconds to one minute, layer 15 is inserted tail end first from the right side of the apparatus (as determined from FIGURE 3) between the rollers 10 and 11, the metal plate 29 is raised off the platen 12, the non-marring, heat resistant layer of material 16 is disposed wrinkle free upon the upper surface on layer and metal plate 29 is placed upon layer 15 and heat resistant layer 16. Forming roller 10' is rotated in a clockwise direction (as determined from FIGURE 3) until the clamping means 3-2 is positioned in close proximity to roller 11 and on the side opposite that of platen 12, as shown in broken lines in FIGURE 3. The metal plate 29 is positioned with the leading edge 29]; thereof being in abutting relation with edge 55a of metal strip 55. The earns 35 and clamping means 32 are rotated in a counter clockwise direction (as determined from FIG- URE 3) until they come in contact with metal strip 56 and force metal strip 55 into firm contact with the outer surface of roller 10. The cams 35 are preferably positioned such that the force transmitted therethrough is concentrated at the place and in the direction indicated by arrow 59 in FIGURE 4, arrow 59 being positioned slightly to the right of edge 55a of metal strip 55 (as determined from FIGURE 4). The purpose of positioning the cams 35 in this manner is to insure that the leading edge 29b of the metal plate 29 is held in firm contact with the outer surface of roller 10. The cams 35 are preferably positightened one at a time, preferably starting first with the center cam and so on until all the cams have been rotated and tightened down. The cams 35 preferably should be mounted and actuated in such a manner as to insure that they will not move out of contact with or otherwise exert less force upon the metal strip 56 during the forming operation. When the cams 35 are mounted and actuated as described above, there is no tendency for them to become unloaded or to exert less force on metal strip 56 during the forming operation, rather the tendency is just the opposite since the movement of the roller 10 is a counterclockwise direction (as determined from- FIGURE 3) during the forming operation exerts a force upon each cam 35 which tends to rotate said cams in the counterclockwise direction and thereby further increases the amount of force being exerted by each cam 35 against metal strip 56.

Forming roller 10 is rotated until the trailing edge of the non-marring, heat resistant layer of material 16 has passed by rotatable cam 13 and the trailing edge 29c of the plate 29 has completely passed between rollers 10 and 11, and preferably until the trailing edge 290 of the plate 29 has traveled for a distance of several inches beyond the opposed surfaces of rollers 10 and 11. At this time rotatable cam 13 is actuated by rotating cam handle 27 preferably in a counter clockwise direction (as determined from FIGURE 1). Actuation of cam 13 Wedges the trailing edge of layer 15 firmly against the upper surface of platen 12, thereby preventing further movement of same along the upper surface of plate 12. Rotata-ble cam 13 is preferably actuated as described so as to insure that during the last phase of the forming operation it will not exert any less force upon the trailing edge of layer 15. If cam 13 were actuated by rotating same in the opposite direction, i.e., clockwise as determined from FIGURE 1, continued rotation of forming roller 10 would tend to decrease and could completely remove the force being applied to the trailing edge of layer 15 through cam 13 by causing cam 13 to rotate in a counter clockwise direction. Since forming roller 10' continues to rotate until the clutch assembly 19 slips at a predetermined torque level, all the slackness in layer 15 is taken up through the application of the tractive force being applied thereto and a consequent increased forming pressure is thereby applied to the plate 29 to hold same in firm contact Within the outer surface of forming roller 10. Preferably, the tractive force being applied to the trailing end of layer 15 is applied in a direction convergent toward the outer surface of forming roller 10 such that a portion of the trailing edge of layer 15 forms an acute angle with the trailing edge 290 of metal plate 29. The motor 17 is shut-off when the clutch assembly 19 begins to slip and as a result of the high frictional force existing within the gear box 18 and the rest of the power transmission system, this tractive force and the increased forming pressure continue to be applied until the forming roller 10 and/ or the rotatable cam 13 is moved in a clockwise direction (as determined from FIGURE 1). Due to the interaction of the layer of material 15 and the tractive force applied thereto, forming roller 10 and a specified ambient temperature, misalignment of the rollers 10 and 11 are of little importance since the amount of forming pressure does not depend solely on the respective positions of these rollers. Thus, the problems associated with normal wear and tear of the machines of this kind have for most purposes been eliminated.

During the forming of metal plate 29, the temperature of the plate is increased from its preheated temperature to a temperature within the hot Working temperature range of the composition of the plate. Elevation of the plate to a temperature within said temperature range may, if desired, take place subsequent to forming of the plate to the new configuration. In the apparatus shown this increase in temperature normally occurs when the plate is brought into close proximity and/or actual contact with the outer surface of the forming roller 10, and since the plate is being fed at a comparatively slow rate between the rollers 10 and 11 and since the time required for heating the plate to a temperature Within the specified temperature range is quite small, seldom exceeding approximately thirty seconds to one minute, the plate normally reaches the desired elevated temperature before the tractive force has been applied to layer 15.

' It has been discovered that the metal plates must be subjected to the forming pressure and the increased temperature a sufficient period of time until substantial recovery has been obtained within the plate structure through the removal of residual stresses by localized plastic flow. subjecting the plate to this pressure and in creased temperature for this period of time results in the formation of a highly dimensionally stabilized plate which will not appreciably change shape when subsequently burned-in and etched. The minimum period of time required for subjecting a curved plate approximately 0.18 inch thick to the forming pressure and increased temperature has been found to be approximately thirty seconds. The maximum period of time depends upon the rate at which grain growth or grain enlargement occurs. As previously discussed, the maximum period of time should be limited to that period in which the maximum grain diameter does not exceed approximately 0.003 inch as determined by the Haynes intercept method.

Following the formation of the plate in the above described manner, the tractive force applied to the layer 15 is released by rotating the forming roller 10 and/ or rotating the cam 13 in a clockwise direction (as determined from FIGURE 1). The cams 35 are then rotated so that layer 15 and the non-marring layer of heat resistant material 16 may be removed. The formed metal plate 29 is then removed from the forming roller and preferably positioned with its longitudinal axis in a vertical plane and then cooled in any suitable manner such as by air quenching or air cooling. The apparatus is then ready for the next plate.

\Vhile the above described process and apparatus has been used to good advantage with various metals to produce curved plates and which have at least the surface to be etched free from objectionable check marks and without appreciably changing the grain size of the metal and which do not appreciably change shape during the burning-in and etching process, i.e., the radius of the etched plate equals the radius of the unetched plate plus or minus 0.005 inch, and normally plus no inches, minus 0.005 inch; excellent results have been achieved with two of the most conventionally used photoengraving metal alloys-zinc and magnesium. Examples of such alloys and their forming temperature are as follows, in which the amounts are expressed in percent by weight;

A. Zinc base alloy:

0.05% to 0.35% aluminum 0.01% to 0.10% magnesium Remainder special high grade zinc 99.99% pure Preheat temperatureabove approximately 135 F.

Preferred preheat temperature-above approximately 150 F but below the hot working temperature range Hot working temperature range-approximately 330 F. to 430 F.

Preferred temperature within the hot working temperature rangeapproximately 360 F.

Period for soaking within the hot working temperature rangeapproximately 30 seconds to 20 minutes B. Magnesium base alloy:

2.5 to 4% aluminum 0.7% to 1.6% zinc 0.08% maximum manganese Small quantities of one or more impurities such as:

silicon, copper, nickel, iron and calcium Remaindermagnesium Preheat temperatureabove approximately 250 F.

Preferred preheat temperatureabove approximately 350 F., but below the hot working temperature range Hot working temperature range450 F. to 800 F.

Preferred temperature within the hot working temperature rangeapproximately 500 F.

Period for soaking within the hot working temperature range-approximately 30 seconds to 30 minutes.

Since metals for photoengraving applications are selected because they possess qualities of hardness, dimensional stability and etchability and since the instant invention improves the dimensional stability properties of metal plates without adversely affecting the other desired qualities, it will be readily appreciated that the instant invention can be used to good advantage whenever dimensional stability in formed metal is an important requisite and that the invention is not limited solely to forming the above described metals or even to metals suitable for photoengraving applications but encompasses metals generally.

Curved plates made in the above manner have an inside diameter which for all practical purposes is the same as the outside diameter of the forming roller. The results of extensive tests show that the curved plates contract, i.e., the radius of curvature thereof decreases, a slight amount following burningin. However, following the etching process, the plates expand or spring back, i.e., the radius of curvature thereof increases, an amount equal to or nearly equal to the amount of contraction that took place during the burning-in. Since a plate having an inside radius equal to or slightly less than the outside radius of the printing drum upon which it is to be used is easier to install, has a longer printing life and produces a better impression than a plate having an inside radius larger than the outside radius of the printing drum, it will readily be appreciated that in view of the characteristics of an etched plate formed according to this invention to assume a radius substantially identical to that which the plate had prior to etching and burning-in, the outside radius of the forming roller should not exceed the outside radius of the printing upon which the plate is to be used. It will also be appreciated that the effectiveness of the illustrated apparatus is not affected by wearing of the bearings or misalignment thereof since the radius of the plate depends only upon the interaction of layer 15, forming roller 10 and a specified ambient temperature. Consequently, the apparatus is not sensitive to wearing of the bearings and the like.

From the foregoing, it will be apparent that the invention provides a dimensionally stabilized curved metal plate suitable for photoengraving applications, such that printers and publishers need no longer maintain expensive metal forming'equipment in order'to make curved etched photoengraving plates.

It is to be understood that this invention is not limited to the exact embodiments of the device shown and described, which is merely by way of illustration and not apparent to those skilled in the art, and it is therefore intended that the appended claims cover all such changes and modifications.

What I claim is:

1. A method of forming a curved zinc alloy plate for photoengraving comprising applying pressure to progressively form a plate to a desired configuration while maintaining said plate at a temperature above F. but below 330 F. to permit formation thereof with at least one surface being substantially free of check marks, and completing the forming of said plate by subjecting said plate to an increased forming pressure and to a temperature within the range of 330 F. and 430 F. for a time period which renders the plate dimensionally stable without a substantial change in grain size.

2. A method as described in claim 1 in which said plate has a composition comprising zinc, 0.05% to 0.35% aluminum, and 0.01% to 0.10% magnesium.

3. A method as described in claim 1 in which during the completion of forming the period of time that said plate is subjected to said increased forming pressure at a temperature within the range of 330 F. and 430 F. varies between approximately 30 seconds and 20 minutes.

4. A method of forming a curved magnesium alloy plate for photoengraving comprising progressively applying pressure to form the plate to a desired configuration while maintaining said plate at a temperature above 250 F. but below 450 F. to permit formation thereof with at least one surface being substantially free of check marks, and completing the forming of said plate by subjecting said plate to an increased forming pressure into a temperature within the range between 450 F. and 800 F. for a time period which renders the plate dimensionally stable without a substantial change in grain size.

5. A method as set forth in claim 4 in which said plate has a composition comprising 2.5% to 4% aluminum, 0.7% to 1.6% zinc, a maximum of 0.08% manganese, and a minimum of 93.5% magnesium.

6. A method as set forth in claim 4 in which during the completion of forming the period of time that said plate is subjected to said increased forming pressure and to a temperature within said range of 450 F. and 800 F. varies between approximately 30 seconds and 30 minutes.

7. An apparatus for forming preheated metal plates comprising a pair of spaced apart rollers one of which is a forming roller, heating means capable of heating at least a portion of the outer surface of said forming roller, driving means for driving said forming roller,

means for urging a plate into contact with the outer surface of said forming roller, said means including a layer of flexible metal, means for removing mounting in spaced apart fixed relation to the outer surface of said forming roller 2. first side of said layer of metal, and means for applying a tractive force along a second side of said layer of metal in a direction convergent toward the outer surface of said forming roller, said second side being opposite to said first side.

8. An apparatus for forming a curved metal plate for photoengraving application comprising, a pair of spaced apart rollers one of which is a forming roller, heating means capable of heating at least a portion of the outer surface of said forming roller, drive means for driving said forming roller, means for progressively urging a plate into contact with the outer surface on said forming roller, said means including a layer of flexible metal, means for removably mounting in spaced apart fixed relation to the outer surface of said forming roller :1 first side of said layer of metal, means for maintaining a portion of said layer of metal in spaced apart relation with the plate, means for securely mounting a second side of said layer of metal in a position substantially inde- 12 pendent of said first side, said second side being opposite to said first side, and means for applying a tractive force along the second side of said layer of metal in a direction convergent toward the outer surface of said formed roller.

References Cited by the Examiner UNITED STATES PATENTS 2,108,822 2/1938 Lippincott 101 395 2,180,293 11/1939 Finkeldey 75l78.2 2,209,674 7/1940 Burish 14813O 2,428,825 10/1947 Arnoldy l48l30 2,763,584 9/1956 Badger 14832 2,788,757 1/1957 Wellborn l48-32 2,841,083 6/1958 Kirkpatrick et al 29-424 3,136,672 6/1964 Prongay lO1-395 FOREIGN PATENTS 594,432 3/1960 Canada.

DAVID L. RECK, Primary Examiner.

O. MARJAMA, H. J. SAITO, Assistant Examiners. 

1. A METHOD OF FORMING A CURVED ZINC ALLOY PLATE FOR PHOTOENGRAVING COMPRISING APPLYING PRESSURE TO PROGRESSIVELY FROM A PLATE TO A DESIRED CONFIGURATION WHILE MAINTAINING SAID PLATE AT A TEMPERATURE ABOVE 135*F. BUT BELOW 330*F. TO PERMIT FORMATION THEREOF WITH AT LEAST ONE SURFACE BEING SUBSTANTIALLY FREE OF CHECK MARKS,AND COMPLETING THE FORMING OF SAID PLATE BY SUBJECTING SAID PLATE TO AN INCREASED FORMING PRESSURE AND TO A TEMPERATURE WITHIN THE RANGE OF 330*F. AND 430*F. FOR A TIME PERIOD WHICH RENDERS THE PLATE DIMENSIONALLY STABLE WITHOUT A SUBSTANTIAL CHANGE IN GRAIN SIZE. 